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physics- gravity revision (weight (Weight is the force acting on an object…
physics- gravity revision
weight
Weight is the force acting on an object due to gravity - it has the unit newtons (N) and acts towards the centre of a gravitational field.
Weight is a non-contact force because gravity exerts its force through a field. An object does not need to be touching the Earth to have a weight.
The weight of an object may be thought of as acting at a single point called its centre of mass. Depending on the object's shape, its centre of mass can be inside or outside it.
The weight of an object and its mass are directly proportional.
weight = mass × gravitational field strength
gravity
Weight caused by gravity is not always obvious. Astronauts on the International Space Station appear to be weightless. However, they are still orbiting the Earth and are within its gravitational field, so they still have weight. They seem to be weightless because both they and the space station are constantly falling towards the Earth.
Gravitational field strength (g) is measured in newtons per kilogram (N/kg). The Earth's gravitational field strength is 9.8 N/kg. This means that for each kg of mass, an object will experience 9.8 N of force
All objects with mass produce a gravitational field. The more mass an object has, the greater its gravitational field will be.
free body diagrams
A free body diagram models the forces acting on an object. The object or 'body' is usually shown as a box or a dot. The forces are shown as thin arrows pointing away from the centre of the box
Representing an object in a free body diagram as a box or a dot
resolving forces
Two forces can be added together to find a resultant force. A single force can be resolved (broken down) into two component forces at right angles to each other.
Vector diagrams
Draw a right-angled triangle to scale, in which each side represents a force.
Measure the lengths of the horizontal and vertical lines. Use the scale for the first line to convert these lengths to the corresponding forces
work
Work is done when energy is transferred from one store to another.
work done = force × distance